Field of the Invention
The invention relates to a system for transferring electric energy to a vehicle, in particular to a track bound vehicle such as a light rail vehicle (e.g. a tram) or to a road automobile such as a bus. The system comprises an electric conductor arrangement for producing an alternating electromagnetic field and for thereby transferring electromagnetic energy to the vehicle. The conductor arrangement comprises a plurality of consecutive segments, wherein each segment extends along a different section of the path of travel of the vehicle.
Description of Related Art
Track bound vehicles, such as conventional rail vehicles, mono-rail vehicles, trolley busses and vehicles which are guided on a track by other means, such as other mechanical means, magnetic means, electronic means and/or optical means, require electric energy for propulsion on the track and for operating auxiliary systems, which do not produce traction of the vehicle. Such auxiliary systems are, for example, lighting systems, heating and/or air condition system, the air ventilation and passenger information systems. However, more particularly speaking, the present invention is related to a system for transferring electric energy to a vehicle which is not necessarily (but preferably) a track bound vehicle. A vehicle other than a track bound vehicle is a bus, for example. An application area of the invention is the transfer of energy to vehicles for public transport. Generally speaking, the vehicle may be, for example, a vehicle having an electrically operated propulsion motor. The vehicle may also be a vehicle having a hybrid propulsion system, e.g. a system which can be operated by electric energy or by other energy, such as electrochemically stored energy or fuel (e.g. natural gas, gasoline or petrol).
WO 2010/000495 A1 describes a system for transferring electric energy to a vehicle, wherein the system comprises an electric conductor arrangement for producing an alternating electromagnetic field and for thereby transferring the energy to the vehicle. The electric conductor arrangement comprises at least two lines, wherein each line is adapted to carry a different one of phases of an alternating electric current. The conductor arrangement comprises a plurality of segments, wherein each segment extends along a different section of the path of travel of the vehicle. Each segment comprises sections of the at least two lines and each segment can be switched on and off separately of the other segments. Each one of successive segments of the conductor arrangement can be connected via a separate switch for switching on and off the element to a mainline. WO 2010/000495 A1 describes the field of invention and possible embodiments of the conductor arrangement in more detail. In particular, the serpentine-like embodiment of the conductor arrangement can also be chosen for the present invention.
In order to improve the EMC (Electromagnetic Compatibility) the segments of the conductor arrangement may be fed by a direct current line. Each segment may comprise an inverter for converting the direct current to an alternating current for producing the electromagnetic field. However, each inverter requires cooling during operation. The effort for manufacturing, installing and cooling a number of inverters which is equal to the number of segments is high. Furthermore, with respect to inverters having solid state switches, such as IGBTs (Insulated Gate Bipolar Transistors), the input voltage on the input side of the inverter is limited to the respective maximum operation voltage of the solid state switches. Instead of a direct current supply line, an alternating current supply line may be used to feed the segments. However, it may also be required to convert the current through the supply line in this case. For example, voltage level and frequency in the supply line may differ from the voltage level and frequency which is required for operating the individual segments. Therefore, converters for converting the voltage level and/or frequency may be used instead of the inverters.
Producing a constant alternating current in the line or lines of the segments has several advantages compared to the operation of the segment at constant voltage. One advantage is that the constant current may be a sinus function of time. This means that only a single frequency of electromagnetic waves is produced. Operating the segment at constant voltage in contrast produces non-sinusoidal functions, which means that harmonics at different frequencies are produced, unless a corresponding filter is provided.
Furthermore a constant current on the primary side (the side of the conductor arrangement along the track) enables to reduce the size of the receiver for receiving the electromagnetic field on the secondary side (the side of the vehicle).